The invention relates to a measuring device and an electrical controller having such a measuring device.
When electrical controllers use delta-sigma modulators for example for A/D conversion, a high-frequency clock signal is typically transmitted to a clock input connection of the delta-sigma modulator. The clock signal can be generated in control electronics or an evaluation unit and routed across one or more plug connections to a printed circuit board on which the delta-sigma modulator is arranged, in order to capture analog signals there. The clock signal typically has a frequency in a range from approximately 10 MHz to 20 MHz. The rise time of an edge of the clock signal should be steep enough to produce as little jitter as possible and not to unnecessarily impair the performance of the conversion. These clock signal properties can lead to undesirable interference emissions.
The invention is based on the object of providing a measuring device and an electrical controller that have preferably low interference emissions.
The invention achieves this object by means of a measuring device having: a delta-sigma modulator configured to take an analog signal as a basis for generating a bit stream; and an evaluation unit that receives the bit stream from the delta-sigma modulator and evaluates the received bit stream, wherein the measuring device has a single data transmission line, the delta-sigma modulator is configured to transmit the bit stream to the evaluation unit via the data transmission line using a transmit clock, and the evaluation unit is configured to reconstruct the transmit clock and/or a phase of bits within the bit stream from the received bit stream and to extract the bits from the received bit stream based on the reconstructed transmit clock and/or based on the reconstructed phase. The invention further achieves this object by means of an electrical controller having the measuring device, which is configured to convert the analog signal into a digital signal, and wherein operation of the electrical controller is controlled on the basis of the digital signal.
The measuring device has a delta-sigma modulator that is conventionally configured to take an analog signal as a basis for generating a bit stream. The delta-sigma modulator may be of 1st, 2nd or 3rd order, for example. In this respect, reference may also be made to the relevant technical literature.
The measuring device further has an evaluation unit, configured separately from the delta-sigma modulator, that receives the bit stream from the delta-sigma modulator and evaluates the received bit stream, for example uses digital low-pass filtering to generate a digital signal having a word length comprising multiple bits. In this respect, reference may also be made to the relevant technical literature.
The measuring device has a single data transmission line between delta-sigma modulator and evaluation unit. In other words, the delta-sigma modulator and the evaluation unit are connected to one another for the purpose of data interchange only by means of a single electrical line.
The delta-sigma modulator is configured to transmit the bit stream, for example asynchronously, to the evaluation unit via the data transmission line using a prescribable or prescribed transmit clock. The transmit clock can be chosen to be between 1 MHz and 10 MHz, for example.
The evaluation unit is configured to reconstruct the transmit clock and/or a phase of the bits of the bit stream from the received bit stream and to extract the bits from the received bit stream or useful bits from the received bit stream based on the reconstructed transmit clock and/or the reconstructed phase. The reconstructed phase may be the phase of the received bits referenced to a clock system of the evaluation unit.
According to the invention, a separate clock signal on a clock line designed specifically therefor is not used. Instead, the evaluation unit synchronizes itself to the bit stream.
The invention is based on the insight that a useable dynamic range of the delta-sigma modulator is approximately 80% of the maximum modulation. If the delta-sigma modulator is used for overcurrent detection, for example, overcurrent disconnection typically begins from this order of magnitude. Up to 80%, a 2nd-order delta-sigma modulator involves no more than approximately 10 identical bits being successively transmitted on the data transmission line. Thereafter, a state change for the transmitted bits typically takes place for normally a single bit. An ensuing bit sequence may have the following appearance, for example:
“ . . . 11111111011111110111 . . . ”
Those bits whose state changes are consistent with a conventional start bit or stop bit and can thus be used for synchronizing the data transmission in the receiver or the evaluation unit, as takes place in the case of asynchronous communication by means of a UART (Universal Asynchronous Receiver Transmitter), for example. Synchronization in the evaluation unit can take place on every edge of the bit stream, for example. In this respect, reference may also be made to the relevant specialist literature on the subject UART.
By omitting the clock line that is conventionally used, it is possible for lines to be saved. Additionally, the interference emission is decreased, since no clock signal is transmitted.
In one embodiment, the evaluation unit is configured to take the received bit stream as a basis for generating a digital signal consistent with the analog signal in digital representation. The digital signal can have a resolution of 8, 16 or 32 bits, for example.
In one embodiment, the evaluation unit has a clock recovery unit configured to reconstruct the transmit clock and/or the phase and/or the bits of the bit sequence and/or useful bits of the bit sequence from the received bit stream.
In one embodiment, the evaluation unit has a digital filter that digitally filters the (useful) bits extracted from the received bit stream. The digital filter can further conventionally perform a sampling rate reduction in order to adjust an oversampling ratio in suitable fashion. In this respect, reference may also be made to the relevant specialist literature.
In one embodiment, the delta-sigma modulator has a clock generator for generating a modulator clock, wherein the delta-sigma modulator is configured to generate the bit stream using the modulator clock. Alternatively or additionally, the delta-sigma modulator can have a clock input connection for supply with an external clock signal, wherein the delta-sigma modulator is configured to generate the bit stream on the basis of the externally applied clock signal.
The invention further relates to an electrical controller having a measuring device as described above configured to convert the analog signal, which maps a motor current, for example, into the digital signal. The electrical controller controls its operation on the basis of the digital signal.
The electrical controller may be a frequency converter or servo converter.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.